Help with ground iterations

[Hoagtech]

The word ground gets thrown around a lot and I wanted to understand the differences in terminology.

Their is earth ground, frame ground, video ground, and just “ground”

On a JAMMA pin out their is “earth ground” on pins 1,2,A,B,27,28,E,F, and “video ground” on pin 14.

When adapting RGBs to BNC there are 4 channels or Red,Blue,Green,Sync and the outside of the connectors are Ground..

My question is what is the difference between “video ground” and “earth ground”?

In my application I will be connecting RGBs from JAMMA and feeding it into an OSSC through a chopped male SCART to BNC cord.

Will I need tie my “video ground” from JAMMA into the ground from each channel of RGBs from my chopped BNC or is their typically a preferred line that carries “video ground”?

[Josh128]

Earth ground is literally the ground ie "dirt". The 240Vac transformer secondary winding that feeds your home or office is literally center-tapped and connected to a rod driven in the dirt at the base of the pole on which it hangs. This same tap is also connected to the neutral lug on your electric meter pan, which is again connected to a rod driven in the dirt near the meter. 3 wires from your meter- hot, hot, neut, then feed into your home breaker panel box, where each hot is connected to different side bus bars in the panel, the neutral wire is connected the neutral bar, and the neutral bar is connected via a wire to the ground bar. The ground bar is bonded (electrically connected) to the metal panel itself, while the neutral bar is not (except through the ground bar). From that point on to the outlets and equipment in your home, neutral and ground are kept separate for safety reasons. The ground of an outlet is normally connected to the chassis or case of whatever is plugged into it, while the neutral, though electrically connected to the ground wire back at the breaker panel, is NOT connected to the chassis or frame.

Many CRTs do not have a connection to earth ground, or are isolated from it via isolation transformer or the power supply for safety reasons (you, by standing on the ground, are connected to it). Video ground is the point that completes the circuit for your video signals. That means for current to oscillate/flow from your R signal wire for example, whatever it is connected to must eventually lead back to video ground. Often times, R, G, B, and sync grounds may be electrically common to each other. If you have a monitor that is not isolated from earth ground, its possible that earth ground and video ground may be electrically common.

You will most likely need to connect your JAMMA video ground to your RGBs video grounds. If you didnt, where else would you be able to connect your RGBs ground signals? On any signal BNC your video sig will be the center pin and the video sig ground will be the outer part. Unless whatever BNC jack you are plugging into is already connected to your jamma harness video ground, you will need to connect it.

[Hoagtech]

Thanks Josh. it sounds like I do need to tie JAMMA video ground into each ground including sync then.

For a bonus. I am trying to use the VGA input on the OSSC to avoid sync issues with my Taito F3.

I have a VGA breakout on route and was wondering if I need to tie Shield R,G,B as video ground or if I can just use the ground pin to Jamma ground wire?

Also can I tie sync or do I need to run a full sync combiner circuit?

There are more than a few Dsub pinouts, but this is the one I wanted to use on my AV3 OSSC input:

[Josh128]

Ground and RS, GS, BS should all be tied / connected together and connected to the JAMMA video ground pin 14. Check and see if they are all common and if they are, just one tied to the JAMMA pin 14 should work I think.